Esterle, Thomas F.
Investigation into the internal sturcture of mesoporous metals.
University of Southampton, Chemistry,
Nanostructured metal films were electrodeposited through the hexagonal lyotropic liquid crystalline phase (H1). The mesoporous structure consists of porous channels (a few nm in diameter) arranged in an hexagonal array. These mesoporous metal films exhibit high surface areas supplied by the concave surface within the pores. The properties of these mesoporous materials have been investigated to gain an insight on the mesoporous structure. Cyclic voltammetry in acid of H1 mesoporous Pt is similar to polycrystalline Pt made up of low index Pt facets. However CO stripping voltammetry shows differences between the H1 mesoporous Pt and polished Pt electrodes. The CO stripping voltammogram for the H1 mesoporous Pt electrode exhibits a CO oxidation pre-wave and CO oxidation at lower overpotentials. These differences result from the presence of trough sites corresponding to the intersection of two pore walls within the mesoporous structure.
The adsorption of foreign atoms Bi and Ge on H1 mesoporousPt was investigated to identify the different crystalline Pt facets. The features of the voltammetric profiles recorded in acid revealed the absence of large (111) domains and the presence of (100) terraces sites. CO stripping voltammetry for H1 mesoporous Pt modified with Bi suggests the presence of a CO-Bi mixed adlayer. However, the absence of the aforementioned pre-wave was attributed to the adsorption of Bi on the trough sites thus causing inefficiency in oxygen transfer for CO oxidation. In contrast, the significant pre-wave observed for H1 mesoporous Pt-Ge leads to an enhancement for CO oxidation.
H1 mesoporous metal films grown on microelectrodes show good stability of the measurement of hydrogen peroxide. H1 mesoporous Rh with a variety of film thicknesses was extensively studied over a wide range of hydrogen peroxide concentrations. A kinetic model is proposed to describe the diffusion of hydrogen peroxide and the surface reaction in the pore. The accessibility of the ionic liquid BMIM-PF6 in the pores was investigated to assess the performance of mesoporous electrodes in supercapacitors. H1 mesoporous Pt of diverse pore size and polished Pt electrodes were characterised in 1 M sulphuric acid and then tested in BMIM-PF6. The double layer capacitances were higher for the H1 mesoporous Pt films thanks to their internal surface area leading to the confirmation that the ionic liquid penetrates into the pores. The analysis of electrochemical impedance spectroscopy shows that the results fit a transmission line model and provides useful parameters for the characterisation of the nanostructured Pt film in BMIM-PF6.
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